Tensegrity structures can give a new approach to the construction of mobile robots with different shapes and properties that usual robots, wheeled or legged, do not have. Tensegrity are light, deformable structures that may be able to adapt their form to unconstrained environments. The main issue of this paper is to present the dynamic equations of motion for such structures, analysed from a Lagrangian point of view, and thinking in using them as mobile robots of arbitrary form and size.